1. Field of the Inventions
This invention relates to a system for rapidly producing a plastic part from a curable liquid which is capable of solidification when subjected to ultra-violet light energy and more particularly to an erasable mask for reflecting ultra-violet light energy onto the curable liquid by frame-by-frame exposure in order to produce the plastic part.
2. Description of the Prior Art
In the production of a plastic part it is common to first design the plastic part, then produce a prototype of the plastic part and finally review the design of the plastic part. This involves considerable time, effort, and expense. This process is repeated until the design of the plastic part has been optimized. After design of the plastic part has been optimized it must be produced. Most plastic parts are injection molded. Since the design and tooling costs of molds are very high, plastic parts are usually only practical if the production volume is high. While other processes are available for the production of plastic parts, including direct machine work, vacuum-forming and direct forming, such methods are typically only cost effective for short run production and these plastic parts are usually inferior in quality to molded plastic parts. In recent years techniques have been developed for generating a plastic part within a curable liquid which is selectively cured by beams of radiation brought to selective focus at prescribed intersection points within a three-dimensional volume of the curable liquid.
European Patent Application No. 87304865.6, entitled Three-Dimensional Modelling Apparatus, filed on June 2, 1987, teaches a modelling apparatus which includes a part generator, a workstation and a processing center. The workstation and processing center interface with a processor and computer aided design software, such as GEOMED of General Electric/Calma, CADS of Computervision, UNIGRAPHICS of McAuto, MEDUSA of Prime Computer or CIS. In his article entitled "Engineering without Paper," published in High Technology, in Mar. 1986, John K. Krouse describes and lists these computer aided design software programs. The workstation and processing center also provide an output to the part generator. The part generator includes a receptacle for the curable liquid, a source of ultra-violet light energy, a beam modulator and deflector. A reservoir supplies the curable liquid through a digitally controlled pump so that the curable liquid continues to lie in a solidification plane within the receptacle. The source of ultra-violet light energy may be either a laser or a strong arc lamp. The beam modulator and deflector receives data in raster forms, vector form or a combination of both. The curable liquid may be any suitable radiation polymerizable liquid which is commonly used in the coating and printing industries. The source of ultra-violet light energy may project an exposure through an erasable mask. The erasable mask may be either line-by-line exposure using an electro-optical shutter, such as a light switching array, or frame-by-frame exposure using a light valve in the form of a planar array, such as a liquid crystal display array. Unfortunately there are no light valves suitable for selectively allowing ultra-violet light energy to pass through because the planar array which must record and then erase images will be damaged by ultra-violet light energy which must pass through it in order to be projected onto the curable liquid in the solidification plane. Although line-by-line exposure is much slower than frame-by-frame exposure, the lack of a suitable light valve for ultra-violet light energy inhibits implementation of frame-by-frame exposure. The source of ultra-violet light energy may also project an exposure through a segment of a strip of film so that it impinges on the curable liquid in the solidification plane. The configuration of each layer of the plastic part is photographically recorded on one of the film segments. Each film segment has a micropositioning pattern thereon, such as perpendicularly extending Ronchi rulings, to align the layer of the plastic part with its preceding layer. Although the film segments provide frame-by-frame exposure and are suitable for ultra-violet light energy the use of the strip film is slower than use of an erasable mask providing frame-by-frame exposure.
U.S. Pat. No. 4,575,330, entitled Apparatus for Production of Three-Dimensional Objects by Stereo-lithography, issued to Charles W. Hull on Mar. 11, 1986, teaches a stereolithographic system which produces a plastic part from a curable liquid which solidifies when subjected to ultra-violet light energy. The stereolithographic system uses a source of ultra-violet light energy to provide a programmed movable spot of ultra-violet light energy on the surface of the curable liquid. The spot of ultra-violet light energy is moved either using cross-axis galvanometers with attached mirrors or an X-Y arm which moves the source of ultra-violet light energy. Each cross-sectional lamina is solidified on the surface of the curable liquid serially by scanning the spot of ultra-violet light energy directly on the curable liquid. U.S. Pat. No. 4,100,141 teaches a curable liquid which solidifies when subjected to ultra-violet light energy.
In his article entitled "Automatic Method for Fabricating a Three-Dimensional Plastic Model with Photo-hardening Polymer," published in Review of Scientific Instruments, Volume 52, Number 11, in Nov. 1981, Hideo Kodama discloses a system which automatically fabricates a plastic part by exposing a liquid photo-hardening polymer to ultra-violet light energy to create a plurality of cross-sectional solidified laminae and serially stacking the cross-sectional solidified laminae to form the plastic part. In his article entitled "Solid Object Generation," published in Journal of Applied Photographic Engineering, Volume 8, in 1982, Alan J. Herbert discloses a similar system which only fabricates a plastic part which is a solid of revolution.
U.S. Pat. No. 4,041,476, entitled Method, Medium and Apparatus for Producing Three-Dimensional Figure Product, issued to Wyn Kelly Swainson on Aug. 9, 1977, teaches an apparatus in which a plastic part is formed in situ in a medium having two active components by causing two radiation beams to intersect in the media. The beams trace surface elements of the figure product to be produced.
U.S. Pat. No. 4,078,229, entitled Three Dimensional Systems, issued to Stephen D. Kramer and Wyn K. Swainson on Mar. 7, 1978, teaches a method for producing plastic parts by the intersection of radiation beams.
U.S. Pat. No. 4,238,840, entitled Method, Medium and Apparatus for Producing Three Dimensional Figure Product, issued to Wyn K. Swainson on Dec. 9, 1980, teaches a method for forming a plastic part in situ in a liquid having two active components by causing two radiation beams to intersect in the media. The beams trace surface elements of the plastic part to be produced.
U.S. Pat. No. 4,288,861, entitled Three-Dimensional Systems, issued to Stephen D. Kramer and Wyn K. Swainson on Sept. 8, 1981, teaches a multiple beam absorption effect which creates plastic parts from a liquid medium. Two beams of optical electromagnetic radiation of a spectral characteristic which is matched to the excited state properties of the molecules of the active liquid medium may be either simultaneously or sequentially directed to a common target location to effect a desired photochemical reaction. U.S. Pat. No. 2,381,234, U.S. Pat. No. 2,525,532, U.S. Pat. No. 2,775,758, U.S. Pat. No. 3,609,707, U.S. Pat. No. 3,723,120, U.S. Pat. No. 4,081,276, U.S. Pat. No. 4,252,514 and U.S. Pat. No. 4,466,080 are other relevant patents.
U.S. Pat. No. 4,391,499, entitled Image Projector, issued to William C. Whitlock on July 5, 1983, teaches an image projector which creates a three-dimensional image. The image projector includes a plurality of modules which are controllably illuminated to form the desired display. The modules are formed to be illuminated and to pass light from within through their walls and to prevent light from entering their outer walls when the modules are not illuminated.
In an article, entitled Optical Processing with the Ruticon, written by Nicholas K. Sheridon and Michael A. Berkovitz, published in SPIE, Volume 83, Optical Information Processing, Ruticons are optically addressed light valves for image storage and optical processing applications. A wide range of image storage times and sensitivities are obtainable depending upon the desired applications.
U.S. Pat. No. 3,716,359, entitled Cyclic Recording System by the Use of an Elastomer in an Electric Field, issued to Nicholas K. Sheridon on Feb. 13, 1973, U.S. No. 3,842,406, entitled Cyclic Recording System by the Use of an Elastomer in an Electric Field, issued to Nicholas K. Sheridon on Oct. 15, 1974, and U.S. Pat. No. 3,853,614, entitled Cyclic Recording System by the Use of an Elastomer in an Electric Field, issued to Nicholas K. Sheridon on Dec. 10, 1974, teach applications of Ruticons, which are elastomers, to various imaging techniques which may be used for the cyclic recording, storage and subsequent erasure of optical information to form images by the elastic deformation of a thin elastomer layer. The pattern of the surface deformation, in general, follows the light distribution of the optical image being recorded. This image is formed on a photoconductive layer which is adjacent to, or integral with, the elastomer layer. An electric field is placed across the elastomer and the photoconductor layers so that the field is modulated by the action of the image light on the conductivity of the photoconductor to provide the mechanical force necessary to deform the elastomers. Once the elastomer surface has deformed, it will in general remain deformed as long as the field across it is maintained. The image recorded is stored. Removing the electric field allows the elastomer to relax and the image is consequently erased. Reversing the field increases the rate at which the image is erased. A new image may now be formed and the cycle started over again. Such an elastomer material is capable of a great many recording/storage/erasure cycles.
U.S. Pat. No. 4,023,969, entitled Deformable Elastomer Imaging Member Employing an Internal Opaque Deformable Metallic layer, issued to Nicholas K. Sheridon on May 17, 1977, teaches an imaging member of an imaging system which includes a pair of deformable layers and a deformable metallic layer which is arranged between the pair of deformable layers. At least one of the deformable layers includes an elastomer material. In operation an electrical field is established across the deformable layers to cause deformation thereof in imagewise configuration. The imaging member may include photoconductive material and may include a pair of electrodes for establishing an electrical field across the deformable layers. The electrodes include an electrical x-y matrix address system.
U.S. Pat. No. 4,111,538, entitled Projection System of High Frequency, issued to Nicholas K. Sheridon on Sept. 5, 1978, teaches a light system for projection of images onto a visual read out surface such as a screen or photo receptor recording device such as a xerographic drum. The projection system employs a non-point light source which forms a light beam of non-uniform intensity. The light beam is passed through a conical light pipe with a high degree of internal reflection which diffuses the light beam, thereby reducing the non-uniformity of the light beam and also collimates the light beam by internal reflections. The collimated light beam is then modulated with imaging information and is focused onto a visual readout surface such as a screen or a recording device surface.
U.S. Pat. No. 3,932,025, entitled Imaging System, issued to Andras I. Lakatos and John B. Flannery on Jan. 13, 1976, teaches an imaging system which forms a plurality of images on the same surface. The imaging system includes an electro-optic imaging member which includes a voltage or current-sensitive light modulating layer, a layer of photoconductive material which exhibits persistent photoconduction properties and a layer of material capable of generating photoinjection currents when struck by radiation which it absorbs.
U.S. Pat. No. 4,099,262, entitled Automatic Memory Control Feedback System for a Cycling Optical Imaging System, issued to Clark I. Bright on July 4, 1978, teaches a system which alters the deformation of a cyclic imaging member. The system includes a deformable member and a circuit. The deformable member has a deformable surface which has been arranged to be placed in an initial deformed position by the application of an input. The circuit is responsive to the extent of the deformation of the deformed surface for altering the deformation of the surface.
U.S. Pat. No. 4,448,505, entitled Arrangement for Addressing Rays or Planes of Light in Space, issued to Paul DiMatteo on May 15, 1984, teaches an arrangement which projects a sequence of coded patterns onto an object surface and which includes a code generator and a single light source. The code generator has a plurality of addressable light attention regions. The single light source irradiates the code generator. Each region of low attenuation resulting from addressing produces illumination of a corresponding part of the projected coded pattern. The code pattern is projected onto the object surface by passing electromagnetic radiation though the code generator. The purely electrical commands address rays or planes of light in space without the need for mechanically moving parts.